1. Field of Technology
This disclosure generally relates to expandable fastener assemblies and methods of using the same.
2. Description of the Related Art
Fastener assemblies are often used to interconnect a plurality of workpieces, such as a stack of plates or other structural members. Conventional fastener assemblies have a bolt and a collar that cooperate to apply a clamp-up force to the workpieces. For example, two workpieces can be joined together by overlapping the workpieces to create a joint. A fastener assembly can be installed at the joint by drilling a hole through the overlapping portions of the workpieces and positioning a rod in the hole. The workpieces are clamped between a head of the rod and the collar. Unfortunately, these types of joints are susceptible to fatigue damage and have undesired electrical properties.
Contaminates (e.g., moisture, chemicals, debris, and other foreign substances) can become lodged between faying surfaces of joints resulting in increased wear and corrosion. Cyclic loading can lead to fatigue problems. The fastener assembly may allow the workpieces to move relative to one another, which may result in fretting, excessive stresses at the interface of the hole and fastener assembly, vibrations, and the like. In aerospace applications, conventional joints may thus have a relatively short in-service life.
Aircraft are often made of lightweight composite structures that are unable to withstand high electrical currents as well as their metallic counterparts. Composite structures may be damaged by high electrical currents caused by lightning strikes because composite structures do not readily conduct away the electrical currents and electromagnetic forces generated by lightning strikes. Electrical currents tend to not pass through the composites structures (e.g., carbon fiber structures) with poor electrical conductivity and instead pass through highly conductive materials, such as metals. Metal fastener assemblies can conduct electrical currents between layers of composite structures. Unfortunately, loosening of the components of the fastener assembly may result in movement between these components of the fastener assembly, movement of the workpiece, and the accumulation of contaminates at the faying surfaces. These problems may result in arcing or other electrical related problems that may cause fires or explosions. Conventional fastener assemblies may thus be unsuitable for many aerospace applications. Additionally, conventional sleeve/bolt systems have a tendency to cause damage in composite laminates when tolerances stack up to make interferences relatively high. Leading edges of conventional bolts are too abrupt for use with thin-walled sleeves. Shear loading along the holes of composite workpieces may be damaged (e.g., delamination), during installation.